This collaborative project involving laboratories at University California and Purdue University aims to explain the most fundamental growth process in fungi -- formation and development of tubular hyphae by apical growth. Hyphae elongate by a complex mechanism involving massive movement of wall- building vesicles to the apex. In higher fungi, the vesicles and other cell components assemble in the hyphal tip to form a unique and dynamic complex called the Spitzenkorper. The Spitzenkorper occurs only in growing cells, and although it is suspected of playing a central role in apical growth its exact function and the mechanisms that control its action remain unknown. The research will provide crucial experimental tests of a new mathematical/computer model of hyphal growth and morphogenesis, to establish its validity and utility and to determine whether the Spitzenkorper behaves as the vesicle supply center predicted by the model. Accordingly, a mechanism for advancing the Spitzenkorper linearly would generate a hypha. By correlating video-enhanced light microscopy of growing cells with electron microscopy, and cytochemical and immunocytochemical tests, the study will characterize the structure, contents, and dynamic behavior of the Spitzenkorper. Experimental perturbation of the Spitzenkorper in vivo by environmental stresses and by mechanical and electrical perturbation will test its function and the validity of the theoretical model. Genetic mutants will be used to reveal alterations of Spitzenkorper behavior that result in altered patterns of polarity and growth; the biochemical lesions caused by the mutations will provide clues concerning the control of Spitzenkorper behavior. Isolation and characterization of the apical vesicles will allow determination of their biochemical roles in cell growth. The project will explore and integrate key aspects of the cytology, physiology, and biochemistry of fungi to resolve a major outstanding problem in developmental biology.